The present invention relates generally to a hermetic scroll-type compressor and, more particularly, to such a compressor having intermeshing fixed and orbiting scroll members, wherein during compressor operation it is desirable to minimize deflection of the fixed and orbiting scroll members to promote proper sealing therebetween.
A typical scroll compressor comprises two facing scroll members, each having an involute wrap, wherein the respective wraps interfit to define a plurality of closed pockets. When one of the scroll member is orbited relative to the other, the pockets travel between a radially outer suction port and a radially inner discharge port to coney and compress the refrigerant fluid.
It is generally believed that the scroll-type compressor could potentially offer quiet, efficient, and low-maintenance operation in a variety of refrigeration system applications. However, several design problems persist that have prevented the scroll compressor from achieving wide market acceptance and commercial success. For instance, during compressor operation, the pressure of compressed refrigerant fluid at the interface between the scroll members tends to cause deflection, i.e., bowing out, of the scroll members away from the interface. This deflection of the scroll members causes the closed pockets to leak at the interface between the wrap tips of one scroll member and the face surface of the opposite scroll member. Such leakage results in reduced compressor operating efficiency. Furthermore, the stress associated with repeated cycles of deflection may cause weakening and premature failure of compressor components and assembly joints.
Whereas the orbiting scroll member is typically axially reinforced by a driven hub portion, the fixed scroll member includes a plate portion otherwise having no reinforced backing. Consequently, the fixed scroll member is more likely to experience deflection. In a common configuration of a hermetic scroll compressor, a chamber adjacent the back side of the fixed scroll member is defined by the entire back surface of the fixed scroll member plate portion and a housing end portion. If the chamber is occupied by refrigerant fluid at suction pressure, the resulting pressure differential between the chamber and the closed pockets causes outward deflection of the plate portion and its associated leakage. Alternatively, if the chamber is occupied by refrigerant fluid at discharge pressure, the resulting pressure differential causes inward deflection of the plate portion. Inward deflection results in grinding of the wrap tips and face surfaces, which causes friction losses and affects sealing characteristics under varying compressor operating conditions.
In order to prevent deflection of the fixed scroll member, the thickness of the plate portion can be increased and/or stronger materials can be used. However, such an approach to providing stiffness to and reducing deflection of the plate portion tends to increase the size, weight, and expense of the compressor.
Another disadvantage of hermetic scroll-type compressors of the type described herein is the difficulty encountered in assembling a scroll compressor mechanism within a housing. Specifically, the compressor mechanism is typically mounted within a cylindrical central housing portion prior to hermetically sealing the housing by the attachment of opposing housing end portions. This method of assembly requires setting of the air gap between the motor rotor and stator at the same time the compressor mechanism is mounted in the housing. Furthermore, this and other known methods of assembly are tedious and labor intensive, thereby adding to the overall cost and complexity of the scroll compressor.
The present invention is directed to overcoming the aforementioned problems associated with scroll-type compressors, wherein it is desired to minimize deflection of the plate portion of the fixed scroll member and provide an improved method of assembling a scroll compressor.